1. Field of the Invention
This invention relates generally to the filtering of communication signals
2. Discussion of the Related Art
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Since Nikola Tesla built the first radio over one hundred years ago, communication signals, such as electromagnetic (“EM”) signals and/or radio frequency (“RF”) signals have been used extensively for wirelessly transmitting information and/or data from one location to another. For most of the twentieth century, the primary applications for EM waves employed the lower frequency (under 1 gigahertz) signals, such as radio, television, and so forth. Over the past few years, however, higher frequency waves (1+ gigahertz), such as microwave transmissions, have become increasing common in communication applications.
In addition to having the capacity to carry a greater amount of digital information, these higher frequency EM waves are also particularly amenable to being combined and transmitted from point to point as a single “broadband” EM signal. More specifically, information and/or data can be modulated into a plurality of signals, each of which employs one of a plurality of carrier frequencies across a frequency range. For example, with a frequency range between 1 gigahertz and 10 gigahertz, one carrier frequency may use the 1 gigahertz band, another the 2 gigahertz band, and so forth. These single band transmissions (also referred to as “narrowband” transmissions) can be conglomerated together and transmitted together from one location to another as a broadband signal. At the receiving end, a wireless receiver can divide (e.g., filter) the broadband signal back into the plurality of narrowband transmissions, each of which can be demodulated and decoded.
There are a variety of different techniques for dividing or filtering the broadband signal into the one or more narrowband signals. One technique involves modulating the EM broadband signal onto an optical carrier (e.g., a laser) and then filtering out the desired narrowband region from the optical signal with an optical filter. However, optically carrying a broadband signal can introduce relative intensity noise (“RIN”). This RIN can decrease the signal to noise ratio of the narrowband signals, and, thus, can make it more difficult to demodulate and/or decode the narrowband signals. Some systems attempt to suppress the effects of RIN by splitting the optical signal into two parts and then employing a pair of optical filters to filter the signals. Disadvantageously, the two optical filters typically have to undergo a complex balancing and tuning process to work together efficiently. In addition, the pair of optical filters can also occupy a significant amount of space and draw a significant amount of power.
An improved system or method for optically filtering communication signals would be desirable.